1. Field of the Invention
The invention relates to a motor-vehicle clutch having a diaphragm spring supported between a clutch housing and a pressure plate which is prestressed against a flywheel and an adjustment ring rotatably arranged between the pressure plate and the diaphragm spring such that the diaphragm is prestressed against the adjustment ring and the adjustment ring abuts bearing surfaces of supporting protrusions of the pressure plate via supporting surfaces.
2. Description of the Related Art
A prior art motor-vehicle clutch is disclosed in German reference DE 29 20 932 having a diaphragm spring supported between a clutch housing and a pressure plate. An adjustment ring is rotatably arranged on the pressure plate between the pressure plate and the diaphragm spring such that the diaphragm spring is prestressed against the adjustment ring. The adjustment ring of this prior art motor-vehicle clutch has obliquely running supporting surfaces which abut corresponding and likewise obliquely running bearing surfaces of the supporting protrusions of the pressure plate. Three helical springs prestress the adjustment ring in the adjustment direction such that the supporting surfaces of the adjustment ring have the tendency to move relative to the bearing surfaces such that the pressure plate maintains a relatively small distance from its flywheel. This makes it possible to compensate for any play which occurs by a rotation of the adjustment ring. A leaf spring which engages in ratchet teeth of the adjustment ring is intended to prevent the adjustment ring from being able to rotate counter to the adjustment direction. Furthermore, to prevent a return of the adjustment device, the angle of the bearing surfaces and of the supporting surfaces is selected to be small enough for self-locking to occur.
It has been found in practice that, as a result of vibrations, it is often the case that the self-locking which is necessary for the reliable functioning of the automatic adjustment device is insufficient. Such vibrations pass, primarily, via the engine into the motor-vehicle clutch and cannot be totally eliminated in the case of motor vehicles in particular. They may result in adjustment in the normal adjustment direction or counter to the normal adjustment direction.
In particular in the case of motor-vehicle clutches of commercial vehicles, the intention is for the wear volume of the clutch linings to be dimensioned to be as large as possible. This renders lining-wear compensation imperative, because otherwise it would no longer be possible for sufficient compressive force to be applied to the pressure plate by the diaphragm spring of the pressure plate at the end of the lining wear. If the adjustment thus malfunctions, this results in failure of the motor-vehicle clutch, which, in the case of a commercial vehicle, usually involves considerable follow-up costs.